DE 101 39 142 A1 describes an exhaust gas treatment device of a combustion engine, at which a SCR-catalyzer (selective catalytic reduction) is used for reducing the NOx emissions, which reduces the nitrous gases that are contained in the exhaust gas with the aid of the reducing agent ammoniac to nitrogen. The ammoniac is won from a urea water solution that has been sprayed into the exhaust gas area upstream before the SCR-catalyzer in the exhaust gas area of the combustion engine. The urea water solution that has been stored in a storage tank is brought to a default dosage pressure with a pump. For dosing the urea water solution depending on the demand a dosage valve is provided, which is set to a default flow rate.
DE 10 2004 044 506 A1 describes a procedure and a device, at which a reagent that is subject to pressure is also introduced into the exhaust gas of a combustion engine before a SCR-catalyzer. The familiar system uses compressed air for supporting the introduction process, which is conducted through a check valve that provides an opening pressure. A diagnosis of the compressed air pressure is provided, which begins at a starting point of the diagnosis with the closing of the compressed air control valve. It is checked at least at a second point of time, whether the compressed air pressure corresponds with at least one lower threshold, which almost corresponds with the opening pressure of the check valve that has been added to the ambient air pressure. An error signal is provided if the condition is not fulfilled.
DE 10 2005 001 119 A1 describes a procedure and a device, which provide the introduction of an oxidized reagent in form of fuel into the exhaust gas area of a combustion engine upstream before an exhaust gas treatment device, which for example contains an oxidation catalyzer, a particle filter, a NOx-storage catalyzer and/or a SCR-catalyzer, whereby the exhaust gas treatment device or at least part of it shall be heated. A diagnosis of the exhaust gas treatment device is provided by a controlling of the reagent pressure. The reagent pressure that is measured between a reagent safety valve and a reagent metering valve is determined during different conditions of the reagent safety valve and/or the reagent metering valve and is the compared with at least one threshold value. If a threshold is exceeded an error signal is provided.
DE 10 2004 043 366 A1 describes a procedure and device, which again provide the introduction of an urea water solution as an reagent that is subject to pressure into the exhaust gas of a combustion engine upstream before a SCR-catalyzer. An acquainted system provides a supporting of the introduction process by compressed air. The urea water solution that is subject to pressure is conducted into the exhaust gas area of the combustion engine over an introduction pipe. A diagnosis is provided, which checks, whether the introduction pipe is blocked completely or at least partially. The diagnosis is started at a starting time by reducing the reagent pressure as well as the compressed air pressure. The time course of the reagent pressure that has been determined after the starting time is checked with regards to whether a reagent pressure drop occurred. The time course that has been determined after the starting time is also checked with regard to whether compressed air pressure drop occurred. An error signal is provided if the reagent pressure drop as well as the compressed air pressure drop do not fall below a threshold value.
DE 10 2004 022 115 A1 again describe a procedure and a device, which provide the introduction of an urea water solution as a reagent that is subject to pressure into the exhaust gas of a combustion engine upstream before a SCR-catalyzer. This familiar system also provides a supporting of the introduction process by compressed air. A diagnosis of at least one pressure sensor is implemented, whereby a pressure sensor can be arranged in the reagent path as well as in the compressed air path. Ii is checked in at least a first time interval, in which a stationary pressure condition shall occur, whether the pressure signal corresponds at least almost with the stationary pressure. It is checked in at least a second time interval, in which a pressure change occurs, whether the pressure signal almost corresponds with a preset control pressure and/or whether a preset change towards the stationary pressure nearly occurred. An error signal is provided if at least one of the conditions is not fulfilled.
The invention is based on the task to provide a procedure for diagnosing an exhaust gas treatment device and a device for implementing the procedure, which provide a reliable diagnosis result.
The task is solved by the measures that are mentioned in the independent claims.